Various methods have been used to improve physical properties of a polyrotaxane. For example, patent document 1 discloses a method by which physical properties of a polyrotaxane are improved by a method where a hydroxyl group of α-cyclodextrin that is a cyclic molecule is substituted with another functional group. Patent document 1 discloses that substitution of a hydroxyl group(s) of α-cyclodextrin with a hydroxy propyl group(s) or methyl group(s) with a high substitution rate can result in a water-soluble polyrotaxane. However, patent document 1 neither discloses nor suggests bonding a group having a long graft chain to a cyclic molecule.
Further, patent document 2 discloses a crosslinked polyrotaxane in which cyclic molecules (α-cyclodextrins) of a polyrotaxane are crosslinked with each other by using polyethylene glycol. It is further disclosed that, in order to obtain the crosslinked polyrotaxane, polyrotaxane molecules themselves are activated in advance with carbodiimidazole and thereafter a terminal reactive oligomer is added to react with. However, there was a problem that polyrotaxane molecules may be crosslinked with each other when polyrotaxane is activated with carbodiimidazole. Alternatively, there was a problem that a competitive reaction is generated between a residual hydroxyl group of α-cyclodextrin and a terminal hydroxyl group of polyethylene glycol.
More, patent document 3, as described in the patent document 1, discloses a method by which physical properties of polyrotaxane are improved by substituting a hydroxyl group of α-cyclodextrin as a cyclic molecule, with another functional group. Specifically, patent document 3 discloses that when a hydroxyl group of α-cyclodextrin is substituted with a hydrophobic group (ε-caprolactone), the polyrotaxane can result in improved solubility in toluene and ethyl acetate. However, since the substitution reaction of the hydroxyl group(s) with a hydrophobic group(s) (ε-caprolactone) made use of an esterification reaction owing to a ring-opening reaction of lactone, there were problems that reaction conditions, for example, water-inhibiting and high-temperature conditions have to be used and a substituent can not be readily obtained.    Patent Document 1: WO 2005/080469.    Patent Document 2: WO 2002/002159.    Patent Document 3: WO 2007/026578.